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Scaphe Dial
Signed by Alexander Ravillius
Dated 1537; Italian
Ivory; 90 mm in diameter

The compass in the lid has the needle poised above painted and gilt foliate decoration. The circle is divided into 8 winds, marked '[star]' (for north), 'G', '[cross]' (for east), 'S', 'O', 'A', 'P', and 'M', while each wind is divided to 20 and numbered by 5. A glass cover is retained by a brass ring. Slit sights in the ivory rim at the cardinal points form a surveyor's cross, and can be used with the compass to measure magnetic bearings. They have caused open cracks at these points and the rim is now held together by a brass band.

In the scaphe dial in the base the pin-gnomon is set in a turned brass mount at the centre of foliate and circular decorative engraving in the ivory. The glazed magnetic compass at the bottom of the hemisphere is marked with the cardinal points 'O', 'P', 'M' and '[cross]'. The hour lines are numbered 9 to 23, the position of the line for 24 being on the rim, and they are crossed by seven lines for the sun's path between the tropics for the signs of the zodiac, whose symbols are marked on the rim. The hours are marked along the equatorial line. A meridian line within the hemisphere is continued on to the rim, as are the lines for the sun's path. The rim also carried a note of the latitude, 'POLVS G.45' and the signature and date, 'RAVILLIVS M.D.XXXVIII'.

Jim Bennett

Museum of the History of Science, Oxford
Inventory number 36708

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